1. Field of the Invention
The present invention relates to a stirrer organ in composite construction comprised of a metallic part and a hybrid casting, with the hybrid casting being fixed to the metallic part by means of at least one anchoring element which forms a back-cutting in the hybrid casting.
Furthermore, the present invention relates to a method for rehabilitating a damaged metallic stirrer organ which when applied provides a rehabilitated stirrer organ in composite construction.
2. Description of the Related Art
Stirrer organs of this species are applied in particular for stirring of corrosive and/or abrasive media. On account of their extraordinarily high chemical and mechanical stresses, stirrer organs are exposed to severe wear and tear. Until some years ago, these components were therefore made of high-alloy corrosion-resistant steel grades. Since it turned out to be impossible to achieve satisfying service life campaigns with these materials, first efforts have been made some time ago to substitute steel partly by hybrid castings.
Hybrid casting is to be understood hereunder as a mixture composed of a bonding agent and an aggregate. For example, the aggregate is a fine-grain wear-resistant and corrosion-proof material, e.g. silicon carbide, corundum, quartz sand, glass or even blends of these materials. Usable as bonding agents are plastic materials, e.g. epoxy resin, vinyl ester resin or polymethylmethacrylate (PMMA).
The German utility patent DE 201 11 789 U1 describes a stirrer organ in form of a metallic stirrer blade driven by a stirrer shaft. The end of the stirrer blade is provided with a protective cap made of hybrid casting. The protective cap is connected in a form-fit arrangement with the stirrer blade. To this effect, there are boreholes arranged in the stirrer blade which are interspersed with the hybrid casting when the stirrer blade end is cast around with the hybrid casting.
A disadvantage with this type of a form-fit connection between the hybrid casting and the metallic stirrer blade lies in that the hybrid casting is merely retained spot-wise by the hybrid casting webs arranged in the boreholes at the stirrer blade. If the hybrid casting is exposed to heavy loads, stress peaks are thus entailed in the area of the contact points between the borehole and the hybrid casting. The hybrid casting is hereby weakened locally and can be destroyed, whereby the hybrid casting part may at least partly loosen from the metallic stirrer blade.
For anchoring a hybrid casting at a metallic machinery component, it is furthermore known from DE 29723 409 U1 to utilize usual bolts as anchoring elements which are screwed into the metallic machinery component and the heads of which form back-cuttings in the hybrid casting, whereby a strong cohesion is established between the metallic machinery component and the hybrid casting.
This solution bears a drawback in that a large quantity of the hybrid casting must be cast in order to completely enclose the bolt heads. Thus the hybrid casting takes a substantial part of the overall thickness of the composite component. Since the overall thickness of the composite component is defined or at least limited by the hydrodynamic task to be fulfilled, the metallic part can therefore only have a low material thickness. However, since the metallic part represents the load-bearing basis for the composite component, it must be of the highest possible thickness to the benefit of the necessary strength. Large hybrid casting portions in a composite work piece thus frequently entail problems in strength.
Another drawback of this solution also rests in that the hybrid casting is retained by the bolts merely at certain points and spots. If the hybrid casting is exposed to heavy loads, stress peaks are entailed in the area of the contact points between the bolt and the hybrid casting. The hybrid casting is hereby weakened locally so that the hybrid casting part may at least partly loosen from the metallic part.
In view thereof, the technical problem underlying the present invention is to develop a stirrer organ of the species mentioned hereinabove in such a manner that the drawbacks outlined hereinabove are avoided.